Henby coates



H. COATES.

ELECTRIC ARC FURNACE APPLICATION FILED NOV.27, IQIB. v

Patented July 1, 1919. 2 SHEETSSHET I H. COATES.

ELECTRIC ARC FURNACE.

APPLICATION F| LE D Nov 27. 1918.

Patented July 1, 1919.

Z SHEETS-SHEET 2 J usti ng HENRY COATES, OF WAT'FORD, ENGLAND.

ELECTRIC-ARG FURNACE.

Specification of Letters Patent.

Patented July 1, 191a.

.Applicationfiled November 27, 1918. Serial No. 264,392.

To all whom it may concern:

Be it known that 1, Honor CoATns, a subjeet of the King of England,residing in ld 'atford, l-lertfordshire, England, have in vented certainnew and useful Improvements in Electric-Arc Furnaces, of which thefollowing is a specification.

This invention relates to electric arc furnaces and the means wherebythey are regulated. -lt is customary at thepresent time to provide suchfurnaces both with handopcrated means for raising and lowering theelectrodes and with automatic means for adjusting them. Thehand-operated means arebonnnonly employed when the furnace is startedand when approximately stable conditions have been reached the duty ofadthe electrodes is transferred to the automatic gear. Such automaticgear or anton'iatic regulators are both well-known, and are of more thanone kind. The type I of such regulator to which the present invention inpart relates, is that which has its action determined. by the strengthof the current flowing through the arc, and it is hereinafter referredto as an automatic regulator controlled by the current-strength of theare. 1

Automatic regulators of the kind defined, controlled by thecurrent-strength of the are, are sometimes arranged to move theelectrode or electrodes in the direction determined by the automaticcontrol, not with a continuous movement, but by a succession of shortmovements separated from one another by short periods of rest; theobject of this arrangement is to prevent hunting and a regulatorarranged in this manner is hereinafter described as a stepby-stepregulator. I

All automatic regulators of the step-bystep type controlled entirely bythe current-strength of the are are open to the objection that oncertain classes of work, such for example as the melting of turnings andboring s, they do not respond at all times in such a way as to preventtripping the circuit-breaker for the furnace. Each time acircuit-breaker is tripped, and the furnace has to be re-startcd, a lossof time occurs which, in. the case of a reasonably large plant. may beso long as a quarter of an hour, and this loss of time is very objcctionable. The pizcsent invention has for its prime object the obviatingof risk of tripping the circuit-breaker in the said manner but has otherobjects which will hereinafter appear.

According to the present invention there is combined with an arc-furnacean automatic regulator controlled by the current-strength ofthe arc, avoltage-controlled automaticv switch having two or more positionscontrolled bythe voltage at the arc, and means so connecting the switchwith the said regulator that in one position the switch permits the saidautomatic regulator to operate in its normal manner but in the otherposition-coiiperates with other parts of the apparatus so that the areis lengthened at a more rapid rate than by the norn'ial operation of thesaid regulator.

Preferably the voltage-sensitive portion of the said switch isconstructed to move a live contactor between two yieldingly supportedcontact pieces whereof one affords an idle circuit and the otherformspart of the operating circuit for the switch and the parts are soconstructed that the contactor docs-not, when moving in eitherdirection, break circuit with one said contact piece until after it hasmade circuit with the till other. By this means the voltage-sensitiveclosed electro-magnctically on to its contacts in each of its said twopositions. Other features of novelty will hereinafter appear and arepointed out in the claims.

The accompanying drawings illustrate one embodiment of this inventionintended to be employed as an accessory to an automatic step-bystepregulator- F :igure 1 being a front view of the automatic switchportion, and

Fig. 2 a similar view of the voltagesensit-ive'device controlling theswitch of Fig. 1.

The parts are shown in such positions that the switch of Fig. 1. is atthe con'lmencemcnt of the movement called for by the position of theparts of Fig. 2. The switch of Fig. 1 is operated by a solenoid A whoseplunger A carries a yokeA each end of which is linked by a link A to oneof two pivoted switch arms B pivoted at B. Each switch arm B cooperateswith two contacts C and I), and the arm carries a tail piece B on whichis mounted a roller B to cooperate with a cam-track E carried by an armE pivoted at E Beneath each arm E, which constitutes a switch arm, is ayieldingly mounted carbon block F suitable stops and return springs areprovided for the arms E.

Below the yoke A the plunger carries an armature (1 for anelectro-magnetG mounted on the panel below the switch. The yoke A andthe armature G are resiliently connected in any convenient manner to theplunger, as for example through the medium of the coiled spring A*.

To the right-hand side of the panel is a voltage-sensitive devicecomprising a coil H mounted on the center limb of a blocl; of U-shapedstampin gs H between whose polar embrace is a pivoted armature H ofstampings carrying short-circuited coils H Fast upon the spindle of thearmature H is a tongue J constituting a contactor, to play between twocarbon contact pieces J slidingly and resiliently mounted in boxes insuch a way that as the contactor moves away from one in the direction ofthe other, the former .follows it until the other has been reached, butso that continued movement of the contactor causes it ultimately toleave the first said block and break circuit therewith. Suitablecontrols are provided for the armaturel l and some such are indicated bythe dashpot K and counterweight K The coil H is connected by the wiresit across the are which it is desired to control by the meansillustrated. Above the voltage-sensitive device H H is a smallelectrically operated switch comprising a magnet L, its pivoted armatureL and a pivoted switch arm L weighted or spring controlled to tendconstantly to assume the position in which it is shown in the drawing.The free end of the arm L plays between two contacts L L whereof L is adummy,

The electrical circuits of the apparatus are indicated in full lines,chain lines, and dotted lines, indicating respectively, a heavy currentsupply of direct current, a light current control circuit fed withdirect current and a light control circuit fed with aiternating current.

The contacts C are connected by wires 0 to the Thury regulator or handcontrol feed supply and serve to bring supply current controlled by itthrough the switch arms B anud the wires 2) t0 the armature of theelectrode-operating motor. The wires 6' are also tapped into connectionwith the arms E, 'and the carbon blocks F are connected through theirhousings to the two ends of a braking resistance f. The motor has itsshunt field constantly excited independently of the circuits-indicatedin the drawing.

A supply of direct current power at the full voltage at which theelectrode motor carbon J .allel with the wire 7'.

may be operated, is brought by the wires (Z to the contacts D.

From the right-hand contact D two control circuits are taken, the upperone by the wire I through the contact L and the wire a to the solenoidA, from which a wire a continues the circuit to the left-hand contact D.

The other control circuit passes by way of a limiting resistance R tothe contactor J which is thus always alive, and thence by way either ofthe upper or of the l wer In the drawing the path is by way of the lowercontact and the wire j direct to the left-hand main at D. A ta-p pin istaken from the wire j to the coil of the magnet Gr this circuit beingcompleted by way of the wire 9, and the winding of the magnet L to theupper carbon J When the parts are in the position shown in the drawingthe voltage across the arc has fallen to a value below that which it isdesired to maintain and the contactor J has therefore fallen on to thelower carbon block. In this position there is no circuit through themagnets L and G, and the armature of the former therefore drops and itsswitch arm L closes upon the contact L moreover the magnet G being newuneXcited its armature G is free. The plunger A is thereupon pulledupward and the circuit at the contacts C interrupted therebydisconnecting the motor from the ordinary automatic control. As theplunger moves up: ward the rollers B press the arms E on to the contactsF thus momentarily connecting the motor armature to the brakingresistance f and finallythe circuit to the motor armature is establishedfrom the contacts D through the arms B, the brake resistance be ing inthis posit-ion disconnected. The mutor armature is now supplied with anuninterrupted supply at full voltage from the contacts D through thearms B and wires 7). It therefore revolves in the direction to raise theelectrode and does so at the maximum speed obtainable. Meanwhile thecurrent is flowing idly from the right-hand contact D through theresistance R and the contactor J to the left-hand block D. As theelectrode rises and the voltage across the arc increases the contactor Jslowly rises until it meets the upper block J which causes the circuitcomposed of the magnets L and G in series with one another to be put inpar- They are thus, it' energized at all, energized too feeblv to effectany movement of their armatures. Further rise in the voltage at the .arccauses the contactor to rise still further until eventually it breakscircuit with the lower block J. This causes the magnets L and G to befully energized, and the former throws the switch arm L so interruptingthe circuit through the solenoid A. The plunger A thereupon thuspreventing overrunning.

the electrode can In the normal operation of n r-phase furnace lieret.)fore practised without the aid of this invention, and when employed.for the melting down of iron and steel turnings and borings, it isstarted by throwing the autonmtic regulator out of operation and byputting nninuu-i labor on to each of the three electrodes, switching onthe higlrtension side of the usual transformer feeding; the furnace andcarefully and gradually lowering each electrode by the seid n'uinuullabor. In result the charge on the hearth becomes gradually heated andwhen this has proceeded sulhciently :ler for the production of. asubstratum of liquid metal, the duty of controlling the electrodes istrain red from the operatives to the mitomutic regulators It, however,frequently happens tlnit, it cuvity having been formed in the uniss ofthe charge, the material forming the side of such cevity suddenly fallsin siiert-cii- .:uiting the are in. the cavity and cventuelly trippingthe c-ircuit-l'n'enlier. it such tiines tlie tripping of the breaker maybe avoided if "e rnised with sullicicnt rapidity,

It will he observed thut the apparatus provided by this invention mayform it simple addition to existing phmt. switch on the regulutor forraising the electrodc be on elcctro-nnig 'neticully operated switch,then the particular construction of ports shown in 1 may be dispensed.with it desireih and. the ports of li ig. Zbe so counccte l to the saidswitch us to operate it in the inunncr provided. by this invention. Thisinvention enublcs manual control of electrodes to be dispensed with, The

' furnace n'niy thus be started up cold and switched in and out andotherwise handled the ordinary "21y but without the need for menuuludjustment oi the lectrodes zit sl'urting nor subsequently.

If for any reason the supply of power to the timisii'orincr or tinnsloru'icrs supplying the lurnz'ice cut oil", the furnace electrodes will"not. with the nrrnugemeut provided by this invaution. rcmuin close toor in contact with lhe church nor will thcyg (as with the ordinary Thuryregulator under current- C(Hlll'i'll alone teed continuously down intothe furnace -hurgc uniil solid opposition iii-ct witln either Ul whichconditions liable to result in sci'crc short circuits. unless grout cureis exercised by the semi-skilled opera,- tors when reclosiug the switch.

llhe present invention meets these condi- Shoul d the tions by theautomatic raising of the clec trode quite cleur from the chargeim1nedizitcly the voltage is cut oil', until. at the upwnrd limit oftravel of the electrode, at limit switch (either existing or which.could be readily installed) stops this movement automatically;thereafter the mniu switch can be closed and. the electrodes moved downto the charge without dung-er of serious short circuits.

A further advantage results from the fact that the loud variation onautomatic furnace regulators oi the kind in which the control isdependent onv the currcnt-streugth of the arc, is sometii'ncs obtained.by on urrungg'cmcnt in. which the combined current in. the rcgulutorcoil and a loud adjusting circuit is kept in u predetermined ratio tothe muin furnace current.

.lt sometimes occurs in practice that these iul iustments having beenset for it certain loud current in ouch clcctrmle conditions of thecharge in the furnace ell'erd at content sullicieut for smull currentsbut of lliSullicicnt area for the large current for which the rcgulutorhes been set. The regulator then supplies energy to the electrodemotorto drive the electrode downwurd to obtain :in increusc of current up tothe predetermined; value. and. this frequently results in brokenGlOOid'OllPs. "il'ith. the attachment provided by this iuvcntionucontuctof this nature would result in the electrode being first ruisedand then lowered until the nrciv oi" coutuct had been improved by thenornuil switch permits the said uuton'uitic regulator to o icrute in itsnormal i'nzinner but in the other position cooperates with other partsof the uppninl'us so that the arc is lengthened :it u more rapid ratethen by the nornnil opcl'ution of the said regulzitoiz 2. Appurutusaccording to clziin'iing-cluuse No. 1 wherein the voltage-sensitiveportion of the said switch is constructed to move it live contuctorbetween two yieldingly supported contact pieces whereof one lllil)l(.l8an idle circuit and the other forms part of the operating circuit forthe switch and the ports are so constructed that the eontzictor doesnot, when moving in either direction,

break circuit with one said contact piece until after it has madecircuit with the other, for the purpose described.

3. Apparatus according to claimin -ciause operated by the switch to puta brake for N0. 1 wherein the said switch cont-r0 s a secthe arcmdusting motor on and off tutoond switch closed. eiectro-m'agneticaliy inmatically as the switch passes from one po- 10 each of its said twcpositions for the purpose sition to the other.

5 described. in testimony whereof I affix my signature.

4:. The combination with the switch of claiming-clauses No. l and N0. 3of means HENRY COATEE}.

